Injection drug users (IDUs) are at high risk for blood-borne infections, including HIV, hepatitis B (HBV), and hepatitis C (HCV), due to the sharing of drug injection equipment and other blood exposures. Measurement issues in this domain are crucial but are difficult to address adequately given the limitations of retrospective self-reports. Daily measurements of behavior, although still imperfect, may be more accurate than retrospective accounts. The purpose of this R21 project is to conduct a pilot study in which injection drug users report daily on their drug use and injection risk behavior, using an innovative technique of computerized telephone interviewing (Interactive Voice Response, or IVR). The aims of the project include assessing the feasibility of collecting daily reports from this difficult population, comparing daily reports with retrospective measures of drug use and risk, assessing the completeness of retrospective reports of drug injection partners, describing patterns of injection drug use and risk over time within individuals, and describing episode- and day-level contemporaneous correlates and prospective predictors of individuals' injection drug use and risk. By comparing daily reports to retrospective measures, we can examine some of the ways in which retrospective reports may or may not capture injection drug use and risk behaviors. If we demonstrate that the use of daily IVR is feasible with this population, future studies can make use of IVR as a cost-effective means of measuring injection drug use and risk in IDUs. [unreadable] [unreadable] [unreadable]